Continuous casting and rolling of 6201 aluminum alloy

ABSTRACT

A method of continuously manufacturing a heat treatable aluminum base alloy rod, such as 6201 aluminum alloy rod containing from 0.50 to 0.9 percent silicon, from 0.6 to 0.9 percent magnesium and the balance essentially aluminum, comprising heating the metal to a molten state, continuously pouring and cooling the metal to form a cast bar at a temperature above the temperature at which the alloy metals begin to precipitate, continuously lengthening and reducing the cross-sectional area of the bar in a rolling mill to form rod and reducing the temperature of the rod to a temperature level below the crystallization temperature of the alloy metals within a time period which is short enough to keep the alloy metals from precipitating.

United States Patent [72] inventors Daniel B. Coier 3,011,928 12/1961Kopec et a1 266/3 X Carrollton; 3,266,945 8/ 1966 l-lelling et al...148/ 1 1.5 A Joseph A. Bus, Bremen, both of Ga. 3,333,624 8/ 1967 Coferet a1. 164/87 [21] Appl. No. 824,220 3,349,471 10/1967 Bell et a1 164/87X [22] F l y 3, 1969 OTHER REFERENCES [45] Patented Oct. 19, 1971 ModemMetal A 19 Assignee southwire p y 5, pr. 64, T8200. M7. pp. 54, 56 & 58.

Carrollton, Ga. Primary ExaminerR. Spencer Annear Attorney-Jones &Thomas [54] CONTINUOUS CASTING AND ROLLING OF 6201 ALUMINUM ALLOY 2Claims, 1 Drawing Fig ABSTRACT: method of continuously manufacturing aheat treatable aluminum base alloy rod, such as 6201 aluminum [52] US.Cl 164/76, u rod containing from Q50 to Q9 percent Silicon, f 06 164/87,164/89 to 0.9 percent magnesium and the balance essentially alu- [51]Int. Cl B2211 1 H12 minum, comprising heating the meta] to a moltenstate com [50] Field of Search 164/76, 87, finuously pouring and coolingthe metal to form a cast bar at a 89, 270, 278, 283; 266/3; 148/2, 11-5A temperature above the temperature at which the alloy metals begin toprecipitate, continuously lengthening and reducing [56] Reerences cuedthe cross-sectional area of the bar in a rolling mill to form rod UNITEDSTATES PATENTS and reducing the temperature of the rod to a temperature1,931,912 10/1933 Whitzel 148/1 1.5 A level below the crystallizationtemperature of the alloy metals 2,710,433 6/ 1955 Properzi. 164/283 Xwithin a time period which is short enough to keep the alloy 2,994,3288/1961 Lewis 266/3 X metals from precipitating.

. COOLING 25 TOWER 9 SUMP ROLLING MILL [8 29 13 I 6 2a COILERPATENTEDUBT 19 l97l 3,613,767

CASTING Daniel B. Cofer BYJOSQph A Bass yd'wm 4* m ATTORNEYS INVENTORS.

CONTINUOUS CASTING AND ROLLING OF 6201 ALUMINUM ALLOY BACKGROUND OF THEINVENTION 6201 aluminum alloy is a high-strengthaluminum-magnesium-silicon alloy which in wire form and in theheat-treated condition has a tensile strength of over 46,000 p.s.i.,elongation greater than 3 percent, and an electrical conductivitygreater than 52.5 percent IACS. In the past, 6201 aluminum alloy redrawrod and similar aluminum alloy redraw rods have been manufactured forcommercial use by a plurality of separate steps which include DC castingan aluminum ingot, reheating the ingot to about 700 to 850 F., hotrolling the cast ingot to redraw rod, and solutionizing the rod at atemperature of approximately l,000 F. and water quenching the rod. Therod is cold drawn to form wire, and the wire is artificially aged attemperatures between 250 and 450 F. This procedure is capable ofproducing wire having tensile strength and electrical conductivitycharacteristics which are similar to or in excess of those for 6201aluminum.

While the foregoing procedure produces an acceptable product, this batchprocess, or noncontinuous casting process, is capable of producing onlya limited amount of rod; that is, a given sized billet will product onlya corresponding mass of rod, and the lengths of separately produced rodmust be welded together to form longer lengths of rod. When the billetis reheated and rolled to form rod, it is customary to crop the leadingend of the rod since it is of inferior quality. Thus, a

substantial amount of waste is experienced in the former procedure. Anelongated rod which comprises several lengths of batch produced rodswelded together will include poor grain structure at the places where itis welded together, which effects tensile strength and conductivity.Furthermore, it is virtually impossible to create identical conditionsin the reheating and rolling of different billets, and the lengths ofrod welded together will usually have difierent grain characteristics.

In order to reheat the rod in the prior art system, the rod must becarefully handled in order to achieve uniform heating and in order toproduce a uniform product. For instance, the oven into which the rod isplaced for solutionizing must create relatively even heat distributionin order that the rod be uniformly heated. Furthermore, the rod usuallymust be arranged so that there is enough circulation of the air or gasesin the oven between the coils to assure proper heat distribution. It iscustomary to place individual coils of rod on portable racks which spacethe coils from each other for this purpose; however, the racks occupyspace in the oven and reduce the volume of rod that can be heated. Whilethe purpose of reheating the rod is to solutionize the rod, it isdesirable to keep the rod from reaching a temperature substantiallyhigher than its solutionizing temperature since the overlapping portionsof the rod in the coils of rod tend to become tacked or welded to eachother. This tacking together of the portions of the rod creates surfaceblemishes on the rod when pulled apart, and frequently the coils remaintacked together so that several coils of rod tend to pay out together.Thus, even heat distribution within the solutionizing oven is apractical necessity so that the rod can be rapidly and uniformlysolutionized to hold the hazard of rod tacking to a minimum.

The prior art process provides a substantial amount of time in which thealuminum can oxidize, as when the cast ingot cools or is being reheated,when the rod from the rolling mill cools or is being reheated forsolutionizing, and when the solutionized rod from the reheating ovencools. The result is that the rod becomes substantially oxidized, whichmakes it relatively hard for redrawing purposes, and which causes therod to have a relatively dull finish. Of course, when the rod is morehighly oxidized and harder, it is more difficult to draw and the drawdies deteriorate rapidly. Thus, the separate steps required in the priorart process of forming 6201 aluminum alloy rod are expensive in thatseparate handling of the rod is required between and during each step,the product must be handled in a careful manner, and extra equipmentmust be available and maintained to handle the product.

SUMMARY OF THE INVENTION Briefly described, the present inventioncomprises a method of continuously manufacturing aluminum base alloyrod, such as 6201 aluminum rod, without the necessity of reheating theingot or the rod during the process. The bar emerging from the castingmachine is passed through a rolling mill, a quench tube, and then coiledin a continuous process. The heat of the cast bar emerging from thecasting machine is not dissipated and the bar temperature is maintainedin the solutionizing temperature range of the metal as the rod is passedto the rolling mill. The rod is hot worked in the rolling mill andquenched immediately as it emerges from the rolling mill so that thetime lapse from the point where the bar enters the rolling mill to wherethe rod is quenched to a temperature level below the crystallizationtemperature of the alloy metals is less than the time required for thealloy metals to precipitate to the grain boundaries of the metal. Afterthe rod is quenched it is at a temperature below the temperature whereimmediate and substantial precipitation occurs, which provides forsufficient time in which the rod can be drawn into wire or otherwisetreated. When the rod is subsequently cold-drawn into wire it has anunusually high tensile strength and relatively high electricalconductivity, and an unusually bright appearance.

Thus, it is an object of this invention to provide an improved methodfor producing aluminum alloy products.

Another object of this invention is to provide a method of continuouslymanufacturing aluminum alloy rod without the necessity of reheating aningot or the rod to produce a product having high tensile strength andhigh conductivity charac teristics.

Another object of this invention is to provide an improved 6201 aluminumproduct and a method for forming such a product.

Another object of this invention is to provide an economical andexpedient method of manufacturing 6201 aluminum rod.

Another object of this invention is to provide an improved 620l aluminumproduct with a more uniform heat treat along its entire length. Otherobjects, features and advantages of the present invention will becomeapparent upon reading the following specification, when taken inconjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic side elevationalview of a casting machine, rolling mill, quenching tube, and coiler,utilized in the procedure herein set forth.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularlyto the drawing, in which like numerals indicate like parts throughoutthe several views, FIG. ll shows casting machine 10, rolling mill l1,quench tube assembly 12, and coiler 13. In summary, the process of theinvention comprises pouring molten metal from a furnace (not shown) intocasting wheel 10a of casting machine 10. The molten metal is cooled andsolidified in casting wheel 10a and extracted as a solid bar 15 andguided toward and through rolling mill 11. The product is lengthened andreduced in its cross-sectional area within rolling mill 11, and emergesas wrought rod 16. Rod 16 is passed through quench tube assembly 12which includes first stage quench tube 18, pinch rollers 19, secondstage quench tube 30, pinch rollers 21, and rod conduit 22. The rodemerges from rod conduit 22 and is formed into coils by coiler 13. Pump24 receives the quenching liquid from sump 25 and pressurizes firststage quench tube 18. The quenching liquid is passed through quench tube18 in a direction of flow which is along the path of travel of rod 16and is passed through a conduit system to cooling tower 26, where it iscooled and recirculated back to sump 25. Pump 28 receives quenchingliquid from sump 29 and pressurizes second stage quench tube 20. Thequenching liquid of the second stage quench tube is passed throughquench tube 20 in a counterflow relationship with respect to themovement of rod 16, and is passed through a conduit system to coolingtower 30 where it is cooled and recirculated back to sump 29. Thus, thequenching liquids are maintained at controlled temperatures during thequenching process.

In more detail, the molten metal processed through the apparatus is aheat treatable aluminum alloy. 1f the product to be formed is to be 6201aluminum, the ranges of silicon and magnesium contents are from 0.50 to0.90 percent, and from 0.60 to 0.90 percent, respectively. The range ofsilicon and magnesium alloys can vary in this metal beyond the range for6201 alloy to 0.2 to 1.3 percent and to 0.3 to 1.4 percent,respectively, if desired. The metal in its molten state is pouredthrough a fiber glass screen into a holding pot maintained at atemperature above 1,200 F., usually at about l,270 F. From the holdingpot, the metal is poured into casting wheel a where it is cooled andsolidified into a cast bar 15. The cast bar is stripped from castingwheel 10a and passed to rolling mill 1! at a temperature high enough sothat the metal is solutionized, usually between 960 to 1,000 F. As thecast bar passes through rolling mill 11, the bar is hot formed andcoated with a soluble oil concentration maintained at about 40percentand at a temperature below 200 F., usually at about 160 F. Rolling mill1 1 includes a plurality of roll stands which compress the cast baralternately from top to bottom and side to side, which functions tolengthen the cast bar and reduce the cross-sectional area of the castbar, so that the cast bar is progressively formed into redraw rod. Thevolume of soluble oil concentration in rolling mill 11 is maintained ata level of about two thirds the volume in a typical continuous castingsystem for EC. rod. The temperature and volume of the coolant applied tothe rod in the rolling mill are adjustable so that when the rod 16emerges from rolling mill 11, the temperature of the rod is at a levelso that the rod is still within its hot fonning temperature range, whichis usually above 650 F., so that the alloy metals have not precipitatedfrom the aluminum. The low volume of coolant applied to the rod in therolling mill requires a higher concentration of lubricant, approximately40 percent solution as compared to approximately 10 percent for an EC.rod system, and the flow is adjusted so that approximately equal flow ofcoolant is maintained at each roll stand.

Immediately upon leaving the rolling mill, rod 16 passes into quenchtube 18 where it is rapidly cooled or quenched by water. Since theportion of rod 16 emerging from rolling mill 11 is at a high temperatureand is highly ductile at this point and unable to withstand significantcompression, pinch rolls 19 are placed between first stage quench tube18 and second stage quench tube 20 in order to reduce the effects ofcompression in rod 16 as it emerges from rolling mill 11. As the rodemerges from quench tube 18, it will have solidified to an extent suchthat it is able to withstand the compression and friction of pinch rolls19; however, the quenching process of the rod is not complete at thispoint. Thus, the rod passes from pinch rolls 19 into second stage quenchtube 20 where a soluble oil solution is used as the quenching liquid andthe quenching procedure is completed. The distance between first stagequench tube 18 and second stage quench tube 20 is small and the rate oftravel of the rod is high enough so that no significant delay in thequenching of the rod is encountered. As the rod emerges from secondstage quench tube 20, it is passed between pinch rolls 21 and throughrod conduit 22, toward coiler l3. Pinch rollers 21 function to eliminateany compression forces in rod 16 as it passes through second stagequench tube 20, and also to urge the rod through arcuate rod conduit 22to coiler 13.

The quenching liquid flows through second stage quench tube 20 in acounterflow relationship in respect to rod 16, which enables the systemto maintain a positive control over the temperature of the rod as itemerges from second stage quench tube 20. The quenching liquid flowingthrough the quench tube 18 can pass either in convergent or counterflowrelationship with respect to rod 16 since a massive volume of quenchingliquid is forced into contact with rod 16, and accurate control over thetemperature dissipation from the rod cannot be maintained atthis point.

The cast bar enters the first roll stand of the rolling mill in thesolutionizing temperature of the metal which is a temperature above thetemperature at which the alloy metals begin to precipitate to the grainboundaries of the metal, and the rod emerges from the second stagequench tube at a temperature below which any immediate substantialprecipitation of the alloy metals occur. This temperature range is fromabout 850 to about 400 F.

The present invention will be more readily understandable from aconsideration of the following examples:

EXAMPLE 1 An alloy with a metal analysis in the holding furnace ofapproximately 0.69 percent magnesium, 0.51 percent silicon, 0.37 percentiron, and the balance essentially aluminum was maintained at atemperature approximately between l,280 F. to l,300 F. The metal waspoured through a fiber glass screen into a holding pot. The metal in theholding pot was maintained in a temperature range of from about l,270 to1,280 F. The metal was cast at a speed of approximately 8,500 pounds perhour on initial start-up, with gradual increases in speed ofapproximately 5 minutes each, to a speed of about 10,000 pounds perhour.

As the cast bar was stripped from the casting wheel, it was maintainedin a temperature range of from about 940 to 960 F. As the cast barentered the rolling mill, it was at a temperature estimated at 940 F.and entered at a casting speed of 40-46 feet per minute.

The soluble oil concentration of the rolling mill was about 40 percentand maintained at a temperature of approximately 160 F. The gallon perminute of flow of soluble oil was estimated at gallons per minute andall the roll stands had approximately equal coolant flow. Thetemperature of the rod leaving the rolling mill was in the range from675 F. to 725 F. The volume and temperature of the soluble oil solutionin the rolling mill was adjusted to control the temperature of the rodat this point. The rod traveled a distance of less than 8 inches fromthe last roll stand of the rolling mill to the first stage quench tube.The time lapse from a section of the rod entering the first roll standto emerging from the second stage quench tube was approximately 9seconds. The first stage quench tube was approximately 5 feet in lengthand maintained full of flowing cold water in the same direction ofmovement as the direction of movement of the rod. The pinch rolls werehydraulically driven at a speed sufficient to exert tension on the rodextending back toward the rolling mill, which eliminated any twisting ofthe rod in the last three roll stands of the mill and aided in pushingthe rod through the delivery tube. Soluble oil of about 4 percentconcentration in water was circulated through the second stage quenchtube in countertlow relationship to the rod at a rate of approximately150 gallons per minute. As the rod emerged from the second stage quenchtube, its temperature was approximately 250 F.

The rod produced by this method was three-eights inch in diameter, had atensile strength of approximately 25,000 p.s.i. 15 percent elongation,and was of a good commercial quality. No problems were encountered indrawing the rod to 0.067 diameter wire. The rod was drawn after beingallowed to age naturally for 2 days. When artificially aged for 3 hoursat approximately 300 F., the wire had a tensile strength ofapproximately 48,000 p.s.i., 8 percent elongation, and conductivity ofabout 52.5 lACS. The rod showed no more degree of oxidation than does ECmaterial, and the wire drawn from this rod was as bright as EC material,which is very bright when compared to 6201 wire manufactured by thepreviously known processes.

EXAMPLE n The process of example I is substantially repeated except thatthe speed of the casting machine is decreased and the cooling system ofthe casting machine is adjusted so that the cast bar enters the rollingmill at a temperature of 850 F. and requires a time lapse of 30 secondsto emerge from the second stage quench tube in the form of rod. Thevolume of the coolant applied in the quench tubes and rolling mill isadjusted so that the rod emerges at a temperature of 400 F. The wiredrawn from the rod has a tensile strength of over 46,000 p.s.i.,elongation greater than 3 percent, and electrical conductivity greaterthan 52.5 percent lACS. The rod is also very bright.

EXAMPLE Ill The process of example I is substantially repeated exceptthat the metal analysis in the holding furnace is approximately 0.8lpercent magnesium, 0.78 percent silicon, 0.30 percent iron, and thebalance essentially aluminum. The speed of the casting machine isdecreased and the cooling system adjusted so that the cast bar entersthe rolling mill at a temperature of 855 F. and requires a time lapse of19 seconds to emerge from the second stage quench tube in the form ofrod. The volume of coolant applied in the quench tubes is adjusted sothat the rod emerges at a temperature of 390 F. The wire drawn from therod has a tensile strength of over 46,000 psi. elongation greater than 3percent, and electrical conductivity greater than 52.5 percent lACS. Therod is also very bright.

EXAMPLE IV The process of example III is substantially repeated exceptthat the bar enters the rolling mill at 900 F. and leaves the secondstage quench tube at 250 F. in a time lapse of 12 seconds. The wiredrawn from the rod has a tensile strength of over 46,000 p.s.i.,elongation greater than 3 percent, and electrical conductivity greaterthan 52.5 percent IACS. The rod is also very bright.

It has been found that the temperatures and other conditions in theprocess can be varied within recognizable limits without detriment tothe characteristics of the product. For instance, the temperature of themolten metal in the pouring pot and the metal bar extracted from thecasting wheel appear to have no efiect on the quality of the 6201 alloyrod as long as the temperature is not lowered below the solutionizingtemperature. The critical temperatures of the process appear to be thetemperatures of solutionizing and crystallization, which in the case ofaluminum alloy metals is a range of temperatures since the differentalloy metals apparently crystallize and solutionize at differenttemperature levels. The rod must pass from the metal solutionizingtemperature through the alloy crystallization temperature range in ashort time so that the quenching function is able to freeze the metalsin a substantially homogenized condition. This temperature range isestimated to be above 600 F., in most instances and considered tousually be above about 750 F., and the time lapse should normally beless than 30 seconds; however, these figures vary in accordance with thepercentage of alloy metals in the solution. The temperature of thesoluble oil solution in the rolling mill should be maintainedsufficiently low to carry out its cooling function, but can vary to atemperature as high as 200 F., or even higher if enough volume ofsolution is forced into contact with the rod to sufficiently cool therod. The distance between the rod entrance to the rolling mill and therod entrance to the first stage quenching tube and the resulting timelapse taken for a segment of the rod to travel between these points canbe increased as long as the alloy metals do not have time enough inwhich to precipitate. Moreover, the rolling mill can be run hot to allowthe rod to enter the quench tubes with the alloy metals in solution.

The length of the rod formed by this process is virtually unlimitedsince the process is continuous" The grain structure of the rod issubstantially uniform throughout its entire length since the temperatureconditions throughout the system are malntamed re atively constant. Forinstance, the pouring temperature and the temperature of the productextracted from the casting wheel will be substantially constant, theadjustments made to the flow and temperature of the soluble coolant inthe rolling mill will be small after the system has been started andstabilized. Of course, the rod produced by the continuous system willhave no welded joints. Since there is virtually no time delay betweencasting and rolling, between rolling and quenching, there will bevirtually no opportunity for the product to oxidize. Thus, the productcan be easily drawn into wire, and the drawing dies will not deterioraterapidly as they would when the product has been allowed to oxidize andbecome hard. The appearance of the product is improved over that from abatch process in that it is much brighter and is comparable to E.C. rod.Since the rod is relatively cool before it is coiled, there is virtuallyno opportunity for the rod in overlapping coils to stick or tack toitself, and the rod can pay out without hazard to the operator or theequipment. Also, the rod surface will not become damaged by tacking. Theequipment used in casting and rolling the product is virtually the sameas utilized in the casting and rolling of EC rod, so that very littlespecial equipment is required. For instance, no equipment is required tomove the billets or the coiled rod from the casting apparatus to therolling mill, and from the rolling mill to solutionizing ovens, andsolutionizing ovens are not required. The rod can be coiled in densecoils since it does not have to be reheated and quenched as required inthe old process. The densely would coils can be formed in much largerand heavier packages since the packages do not have to be handled andplaced in the small reheating ovens.

While this invention has been described in detail with particularreference to preferred embodiments thereof, it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinbefore and as defined in theappended claims.

We claim:

1. A method of continuously casting and rolling 6201 aluminum alloy rodcontaining from about 0.5 to about 0.9 weight percent silicon, about 0.6to 0.9 weight percent magnesium and the remainder essentially aluminumcomprising the steps of:

a. pouring a 6201 aluminum alloy into the casting groove of a continuouscasting wheel at at temperature above about 1,200 F.;

. removing a cast 6201 aluminum alloy bar from the casting groove of thecasting wheel and passing the bar to a hot-rolling mill so that the barenters the mill at a temperature of 850 F. to 1,000 F., said bar havingbeen maintained at a temperature of at least 850 F., between the wheeland the mill;

c. hot-rolling the 6201 aluminum alloy bar while coating a soluble oilon the bar as it is rolled, said soluble oil being at a temperature ofless than 200 F.; and

d. quenching the hot-rolled rod immediately after it exits thehot-rolling mill to a temperature of less than 400 F., the time intervalbetween entrance into the hot-rolling mill and completion of quench to atemperature of less than 400 F., being between 9 and 30 seconds.

2. A method of continuously casting and rolling 6201 aluminum alloy rodas defined in claim 1 wherein the step of quenching the hot-rolled rodcomprises:

a. quenching the hot-rolled rod with water in a first quench operation;

b. urging the rod along its path from the first quench operation to asecond quench operation; and

c. quenching the rod with a soluble oil and water solution in the secondquench operation.

2. A method of continuously casting and rolling 6201 aluminum alloy rodas defined in claim 1 wherein the step of quenching the hot-rolled rodcomprises: a. quenching the hot-rolled rod with water in a first quenchoperation; b. urging the rod along its path from the first quenchoperation to a second quench operation; and c. quenching the rod with asoluble oil and water solution in the second quench operation.